As has been succinctly stated in U.S. Pat. No. 5,460,247 and reiterated here, there have been difficulties with brake hoses reinforced with braided wires. In order to accommodate necessary relative motion between the sprung and unsprung masses of a motor vehicle (i.e., the chassis and suspended wheels), suspension mounted hydraulic brakes are connected to the chassis by flexible hydraulic hoses. These hoses are typically fabricated form fabric braid reinforced elastomers.
Standard original equipment of such fabric reinforced flexible brake hoses for motor vehicles expand or swell to some extent under pressure, thus consuming available brake pedal travel which can result in a relatively “soft” feel to the brake pedal. This soft feel reduces the precision of brake modulation by the driver. These conditions are unacceptable in racing cars. For over 30 years, racing cars have been equipped with flexible brake hoses having a stainless steel braid layer over extruded Teflon. These hoses exhibit considerably less expansion under pressure resulting in higher and firmer brake pedal and a larger margin of safety because of more even friction pad wear and more precise brake modulation.
Despite an outstanding record of performance and reliability in racing and off-highway use, these high performance flexible brake hoses have not been certified for highway use because they have been unable to comply with the Basic Motor Vehicle Safety Standard 106, Section 56.3 (whip resistance test) set by the U.S. Department of Transportation (DOT).
Past efforts to substitute stainless steel braid protected Teflon flexible hose for the original equipment elastomeric brake hose on vehicles has usually led to fatigue failure of the protective braid at the end of the crimp or swedged collar or socket of the hose end fitting followed by fatigue failure of the Teflon hose and resultant loss of pressure. Consequently, there is a need for flexible brake hose assemblies that accommodate necessary relative motion between the chassis and wheels of a vehicle and passes all aspects of the whip resistance test required by the DOT.
One approach is to remove the stainless steel, braided reinforcement from the hose in the area of a metal coupling, but since the hose is made of polytetrafluoroethylene (PTFE), the hose tends not to meet pressure requirements when exposed to high pressure hydraulic fluid.
Hydraulic brake lines are one recognizable need for the invention, other needs arise when reinforced hoses are attached to other devices which may or may not be connected by tubes.
While hoses made of PTFE have difficulties with respect to DOT tests, there is also a need to improve fluid couplings for hoses of other materials, such as polyethylene, polypropylene, polyamide (NYLON®), PTFE alloys and the like so that hoses of these materials will pass DOT tests. In addition there is a need to make these types of brake hoses less expensive while maintaining their attractive appearance for use on vehicles such as motorcycles. In addition, there is a need to improve strain relief elements used with the brake hoses.